The present invention relates to a direct-light-type planar light source apparatus and a liquid crystal display device.
Liquid crystal display (LCD) units have been widely used for image display in personal computers and various other monitors. A liquid crystal display generally has a liquid crystal panel provided with a driving circuit and a backlight unit disposed at the back side of the panel. The liquid crystal panel displays an image by controlling the transmitted light of the panel. The liquid crystal panel has a display area configured by a plurality of pixel portions arranged in a matrix and a circumferential area formed on the circumference of the display area.
Two general types of backlight unit in a liquid crystal display are the sidelight type and the direct-light type. In the case of sidelight-type backlight, a light source (cold-cathode tube) is set to one side of a light-guide plate (display face); an advantage of this arrangement is that the backlight unit can be decreased in thickness. However, the sidelight-type backlight has the disadvantage of relatively low brightness.
In the case of a direct-light-type backlight unit, a light source is positioned facing a liquid crystal panel; that is, directly under the liquid crystal panel. Therefore, at the expense of increased unit thickness, it is possible to set a plurality of light sources and thereby increase the brightness. The sidelight-type backlight is mainly used in notebook-type personal computers and the direct-light-type backlight unit is mainly used in stationary displays.
The liquid crystal display disclosed in Published Unexamined Patent Application No. JP4-336527 may be characterized as a conventional liquid crystal display using a direct-light-type backlight unit. This arrangement is shown in FIG. 3. A liquid crystal panel 101 is held by a structure 102, and a diffusion plate 104 and a film 105 are fixed to structure 102. Film 105 has a pattern formed therein for providing a uniform brightness. Fluorescent lamps 103 are fixed opposite structure 102 and a reflection plate 106 is fixed to the structure 102 by a tapping screw so as to cover the fluorescent lamps 103. According to the reference, the fluorescent lamps 103 are replaced by removing the tapping screw and removing only the reflection plate 106 from the structure 102.
The above-noted reference does not disclose any details regarding securing the reflection plate by the tapping screw. However, judging from the configuration in FIG. 3, the tapping screw is screwed in the direction vertical to the liquid crystal panel 101 from the reflection plate 106 toward the structure 102. Because the structure 102 supports the liquid crystal display, it is impossible to secure the tapping screw from the front of the structure 102. This increases operations in the fabrication process of the liquid crystal display and decreases the throughput. In the case of the above-described liquid crystal display, the diffusion plate 104 and film 105 are disposed opposite the reflection plate 106. The reflection plate 106 is fixed to the structure 102 by a screw. Therefore, to secure the reflection plate 106 to the structure 102 and thereafter secure the diffusion plate 104 and film 105 to the structure 102, it is necessary to turn the structure 102 inside out. This operation greatly decreases the fabrication throughput.
Moreover, the trend in LCD equipment design is to further decrease the space between the display area and the four outer edges (frame narrowing). Since the conventional liquid crystal display requires space for fixing screws to the sides of a display face, it may not be possible to design the frame as narrow as desired.
It is an object of the present invention to provide a backlight unit and a liquid crystal display capable of improving the fabrication throughput. It is another object of the present invention to provide a backlight unit and a liquid crystal display which permits frame narrowing in the liquid crystal display unit.
An important advantage of the present invention is that it permits very efficient assembly of a direct-light-type planar light source apparatus, lamp replacement, and repair of the display unit. Moreover, the present invention permits design of a narrow frame for the unit. Furthermore, in the present invention a liquid crystal display mode is not adversely affected by fine dust attached to a diffusion plate.
According to a first aspect of the invention, a direct-light-type planar light source apparatus is provided which includes a front frame, a rear frame, and a diffusion plate disposed between the front and rear frames. The apparatus has a light source disposed in the rear frame and facing the diffusion plate. Side faces of the front and rear frames are fixed by removable fastening members. The light source is disposed in the inner space of the rear frame and, preferably, the light source is fixed to the rear frame.
According to another aspect of the invention, a direct-light-type planar light source apparatus is provided as described just above, wherein a light source is fixed to the rear frame. The rear frame and front frame have a rear-frame opening and a front-frame opening on their side faces, respectively. A fastening member (a screw) fixes the rear and front frames by passing through the rear- and front-frame openings. The light source and rear frame can be integrally removed from the front frame by removing the screw.
The above-described apparatus may further comprise a plurality of lamps and a lamp holder for holding the lamps. The lamp holder is fixed in the rear frame.
According to an additional aspect of the invention, the rear frame of the apparatus has a first side member and a second side member. The second side member is formed continuously with the first side member and faces the first side member with a predetermined space between the first and second side members. The rear-frame opening has a threaded structure for receiving a screw and is formed on the second side member. The screw is fixed to the rear-frame opening of the second side member.
According to a further aspect of the invention, the direct-light-type planar-light-source apparatus further comprises a circuit board having a power circuit connected to a light source. The circuit board is disposed on the outside surface of the rear frame.
According to another aspect of the invention, a direct-light-type planar light source apparatus is provided as in the first aspect described above, and wherein the inner face of a rear frame reflects the light supplied from the light source.
A liquid crystal display device according to a further aspect of the invention includes a liquid crystal panel having two transparent substrates and liquid crystal material sealed between the two substrates. The device further comprises a bezel disposed on the display face of the liquid crystal panel and a direct-light-type backlight unit disposed on the side opposite to the display face. The direct-light-type backlight unit has a front frame, a rear frame, a diffusion plate disposed between the front and rear frames, and a light source fixed in the rear frame and facing the diffusion plate. The front frame and the rear frame have a front-frame opening and a rear-frame opening on their side faces, respectively. The front and rear frames are fastened to each other by a screw passing through both openings. The light source and the rear frame can be removed together from the front frame by removing the screw. The bezel has a bezel opening on its side face and a screw can be removed through the bezel opening.
The liquid crystal display device described just above may further comprise a tape carrier package (TCP) connected to an end of a liquid crystal panel. The TCP has a film on which a wiring is formed and a driver IC disposed on the film. The film is folded and the driver IC is disposed in a position facing the side face of a rear frame.